This invention relates generally to surge arresters and more particularly to those arresters known as secondary valve arresters which employ a spark gap portion and a nonlinear resistive material or valve block portion in combination, for dissipating high voltage surges produced commonly by lightning.
In operation, the valve block portion of a secondary valve arrester displays a high resistance to voltages normally carried by the electrical system being protected by the arrester and has a low resistance to voltages in excess of normal system voltage. The spark gap portion of the arrester displays a near infinite resistance until a high voltage surge well in excess of normal system voltage, causes sparkover. Predetermined construction of the spark gap portion can be used to affect the voltage at which sparkover occurs. Accordingly a valve arrester properly constructed for a particular system voltage appears as an open circuit during normal operation and acts as a circuit path to ground during the application of high voltage surges, thereby avoiding damage caused by an overvoltage condition in the system.
It is desirable in valve arresters of the type described that the spark gap portion respond to impulse voltages as low as possible and yet not sparkover at normal system voltage for dissipating quickly high voltage surges which may occur in the system. This is commonly referred to in the art as displaying a good impulse sparkover voltage characteristic.
The provision of such a characteristic has been accomplished through the use of specially designed spark gaps in valve arresters. While these specially designed spark gaps provide the characteristic desired, they are quite elaborate in design and expensive to fabricate.
Valve arresters of the type described are commonly used in single, two and three phase electrical systems. In such cases, each phase of the system includes a spark gap and valve block assembly for protection of that phase. Furthermore, some arresters are constructed for relatively low voltage electrical systems; i.e. 250 volts, while others may be constructed for relatively high voltage electrical systems; i.e. 650 volts. To provide valve arresters for the various uses described normally requires a variety of different arrester embodiments, each comprising a variety of different components. Accordingly, the manufacture of valve arrester embodiments which meet all the requirements of the various electrical systems to be protected, can be costly and the storing of different types of valve arresters requires that a distributor of such arresters maintain a large inventory.